WhatsApp for iPhone multi-device beta now widely rolling out to the stable version1
WhatsApp for iPhone finally getting the long-awaited multi-device support feature
WhatsApp for iPhone version 2.21.180 now has the feature in the section "Linked devices", and although this feature is still in beta, so it is not official, you are able to test it even without being a part of WhatsApp's beta program (which is currently closed for registrations for quite some time). This means, that if you wish to test how this feature works, you can do so right now from your iPhone.
Then, the chat service will take a few seconds to sync your messages, and depending on the number of messages and your message history, the time needed for syncing will vary. Once the syncing is complete, you will be able to use your linked devices independently of whether or not your phone is online or offline. Before this change, the service needed the phone to remain on and online if you're chatting from another device, as it was using it for the end-to-end encryption.
Keep in mind that you can link only up to four separate devices at a time with your account, and none of these additional ones can be phones. You have the right to link only one, main device, which can be a phone, and the other devices can be computers or tablets for example. For now, though, tablets are not yet supported, so you can only link computers: Windows PC or Mac. But this is a welcome addition for people who work on a computer and have two computers (one for work, one for personal stuff for example).
Of course, the feature itself is still in beta, despite it appearing on the stable version, and you have to join the multi-device beta. Given the fact that you will be testing it in a way, WhatsApp advises keeping in mind that not all features might work exactly as intended. One thing that might not work is calling people who are using an old version of WhatsApp from a linked device.
At the moment, there is no information on whether this is a global rollout or is geo-restricted. To check whether you have access to it, make sure you are running WhatsApp version 2.21.180 on your iPhone. If you don't have it yet, most probably you will be getting it soon.
Other helpful WhatsApp features to look forward to
WhatsApp has been working hard in recent months on adding a lot of helpful features and making the chat service as useful and as good as it could be.
Recently we reported on a helpful feature that WhatsApp is currently working on, namely the option to transfer your chat history from an Android device to an iPhone. Currently, there is such a migration tool for iPhone to Android (only Samsung phones are supported though), and soon we might be seeing the opposite migration feature as well.
Additionally, WhatsApp will soon be letting you chose whether or not you want the "Last seen" on your profile to be visible to everyone. This helps you accurately configure who sees your active status on the app and who doesn't.